The Mega Man Zero series is the successor to the Mega Man X story line. 100 years have passed since the end of the Maverick Wars that were front and center for the X series, and Mega Man X and Zero seem to have vanished. A shadowy government begins persecuting Reploids (robots meant to look like humans) by "retiring" them, and a human scientist girl named Ciel seeks out Zero to aid her Reploid comrades.
The game features a very good soundtrack, tweaks on the classic Mega Man gameplay formula, and quite a bit of story. The game is known to be a tad difficult for an introduction, and the newly implemented grading system adds a new element to the series. Kinda.
Original Archived Let's Play available at the Let's Play Archive